Circuit Description

WARNING: This page is about a different car, the 2007 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.

The hvac control module controls the a/c request circuit by grounding the a/c request circuit via an internal solid state device called a driver. The primary function of the driver is to supply the ground for the component being controlled. The driver has a fault line which is monitored by the engine control module (ECM). When the HVAC control module is commanding a component ON, the voltage of the a/c request circuit should be near 0 volts. When the HVAC control module is commanding the request circuit to a component OFF, the voltage potential of the circuit should be near battery voltage. If the fault detection circuit senses a voltage other than what is expected, this DTC will set. This DTC is communicated from the HVAC Control Module to the ECM over the Pulse Width Modulated (PWM) a/c request circuit.

The ECM will monitor the request circuit for the following:

A short to ground
A short to voltage
An open circuit

When the ECM detects any of the above malfunctions, this DTC is set and the affected driver is disabled.